Carburetor



Dec. 20, 1960 H. w. SMITH ETAL 2,955,462

CARBURETOR Filed Jan. 14, 1957 3 Sheets-Sheet l Fig.1.

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INVENTORS /AfioLa W. 5/14/77/ 005527" E. BAR/M55 ATTOQ/VEY Unite States Patent 2,965,462 Patented Dec. 20, 1960 CARBURETOR Harold W. Smith, San Marino, and Robert E. Barnes, Monterey Park, Califi', assignors to American Liquid Gas Corp., Los Angeles, Calif., a corporation of California Filed Jan. 14, 1957, Ser. No. 633,970

17 Claims. (Cl. 48-180) This invention relates generally to charge forming devices or carburetors for internal combustion. engines, and relates more particularly to charge forming devices for carbureting liquified petroleum gases.

While the present invention has particular utility in connection with carburetors for providing a mixture of liquified petroleum gas and air for internal combustion engines, and is shown and described in such connection, it is to be understood that its utility is not confined thereto.

The internal combustion engines in most present day automotive vehicles must operate throughout a wide range of speed, power and other conditions. Engines of this type burn a mixture of fuel and air and the fuel-toair ratio of such fuel mixture should vary under the varying operating conditions of the engine, a rich mixture being required under certain conditions and a lean or leaner under other operating conditions. The mixture, of course, should be that which is most suitable to the engine requirements of each operating condition for the most eflicient, eifective, and otherwise satisfactory use of the fuel under the respective conditions.

Various and special difficulties and problems are encountered in providing carburetors for mixing liquified petroleum gas and air for internal combustion engines, particularly those used to power automotive vehicles and it is an object of the present invention to provide a carburetor which will overcome these various problems and which will improve speed, power and operation of the engine under various operating conditions.

Another object of the invention is to provide a device of this character having jet means which will proportion the fuel-to-air ratio of the fuel mixture according to the demands of the engine.

Still another object of the invention is to provide jet actuated carburetor having improved means which will effect the desired mixing and distribution of the fuel according to the stream of air passing through the induction passage of the carburetor. This object and the immediately preceding object are achieved by the useof a calibrated main fuel metering jet which discharges into a venturi, and by a plurality of fuel jet ports which also discharge fuel into the venturi and are supplied with fuel through novel valve means controlled in accordance with throttle position.

A further object of the invention is to provide an improved idling system in a device of this character.

A still further object of the invention is to provide a device of this character adapted to provide greater economy and efficiency than heretofore. One of the factors in effecting this object is the provision of means which automatically stops the flow of fuel from the idling system to the induction passage under certain conditions of deceleration. This saves fuel, and also reduces exhaust contaminants to a minimum.

The trend of present day automobiles is to lower the hoods and with most such automobiles little vertical space exists under the hood for the downdraft type of carburetor and its air filter which stand upwardly a considerable distance above the top of the engine, and it is therefore another object of the present invention to provide a small, compact carburetor of reduced height so that it will more readily fit under the hood of present day automobiles.

Still another object of the invention is to provide a device of this character that is easy to install.

A further object of the invention is to provide a device of this character that has a main fuel supply system requiring no adjustments, there being an adjustment only for the idle system.

This invention possesses many other advantages and has other objects which may be made more easily apparent from a consideration of the embodiments of the invention shown in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Fig. l is a schematic view of an internal combustion engine equipped with a carburetor embodying the present invention;

Fig. 2 is a top plan view of the carburetor taken on the line 2-2 of Fig. 1;

Fig. 3 is a sectional view taken on the line 33 of Fig. 2;

Fig. 4 is a side elevation partly in section of the carburetor, looking in the direction of the arrow 4 in Fig. 2;

Fig. 5 is a fragmentary sectional view taken substantially on the line 5-5 of Fig. 4;

Fig. 6 is a fragmentary sectional view taken substantially on the line 66 of Fig. 3;

Fig. 7 is a horizontal sectional view taken on the line 77 of Fig. 3;

Fig. 8 is a horizontal sectional view taken on the line 88 of Fig. 3;

Fig. 9 is an enlarged fragmentary top plan view of that portion of the carburetor embraced by the arrows 9-9 in Fig. 8; and

Fig. 10 is a sectional view taken on the line 1010 of Fig. 9.

Referring more particularly to Fig. 1 there is shown an internal combustion engine, indicated generally at 20, having an intake manifold 22. A carburetor embodying the present invention is indicated generally at 23, said carburetor, in the form shown, being of the downdraft type and comprising, as shown in Fig. 3, an air horn section 24 and a throttle body section 25, the adjacent ends of said air horn section and throttle body section being provided with flanges 26 and 27 respectively, secured together by suitable screws 28, with a gasket 28a between said sections. The throttle body section 25 is provided at its lower end with a flange 29 having openings 30 therethrough for reception of screws, not shown, which secure the carburetor 23 to the intake manifold 22 in the usual well known manner.

There is an induction passage which extends vertically through the carburetor and said passage comprises an air inlet 33 and a venturi 34 in the air horn section, an air filter 31 being attached to the upper inlet end of said air horn section in any well known manner. The induction passage also includes a throttle barrel or mixing chamber 35 in the throttle body section 25. A throttle valve 36 controls the throttle barrel 35 in the known manner, said throttle valve being mounted in the usual manner on a throttle shaft 37 journalled in the side walls of the throttle body section. The throttle valve 36 is operable by means of a lever 39 attached to one end of the throttle shaft 37 which extends outwardly of a boss 38 of the adjacent wall of said throttle body section, the lever 39 being provided with an opening 40 whereby an operating means, not shown, may be connected in the usual manner with the lever. A throttle quadrant 42 is secured to the throttle shaft by a screw 43 and one arm of the quadrant is provided with an adjusting screw 45, the inner end of which is adapted to abut against a stop pin 46 fixed in the outer end of said boss 38, said pin 46 being straddled by the arms of said quadrant.

The fuel used is liquified petroleum gas which passes through the usual devices of well known character for reducing the pressure thereof and delivering the gaseous vapor to the carburetor at the desired temperature and reduced pressure, the gas being conducted to the carburetor by a conduit 50 which is connected to the inlet 51 of a chamber 52 defined by a housing 53 attached to a side 54 of the air horn section 24 by means of screws 55, there being a gasket 56 between the inner side of the housing and the side 54.

Fuel for low speed operation is provided by an idling fuel system which has an idle discharge port 60 positioned so as to be below the throttle valve 36 when the throttle valve is in an idling position, for example as shown in Fig. 3. From the chamber 52, fuel for the idling system passes passage 62 in the housing 53, a passage 63a in the air horn section and into a downwardly opening vertical passage 64 in the wall of the air horn section. The passage 64 conducts the fuel into an idle fuel mixing chamber 66 in the adjacent portion of the throttle body section 25. At the upper end of the chamber 66 the upper side of the throttle body section is recessed to receive a plate 68 which has a series of small openings 68a therein through which the fuel from passage 64 flows. From the chamber 66 a bore 70 extends downwardly and communicates with an intersecting downward and inwardly inclined passage 72 which in time communicates at its inner end with the idling port 60. At the outer end of passage 72 there is an enlarged tapped portion 73 for reception of the threaded body 74 of a needle valve, the forward end 76 of the needle valve being somewhat smaller in diameter than the passage 72 and has a tapering forward end 78 cooperating with a valve seat 79 at the inner end of the port 60 to adjust the amount of idle fuel mixture discharged from said port 60. The outer end of the needle valve 74 is provided with an enlarged head 80 for facilitating adjustment of said valve and there is a lock nut 81 on said valve body 74 engageable with the adjacent thickened wall of the throttle body section.

Air for the idling fuel mixture is supplied to the chamber 66 by Way of a downwardly and outwardly inclined passage 85 in the thickened wall of the air horn section, the inlet of the passage 85 being in the air inlet 33 of said air horn section. From the passage 85 there is a downwardly extending passage 87 which communicates with said chamber 66 by way of an opening provided there for in the gasket 28a and a registering opening 68a in the plate 68. The air and fuel for the idling fuel mixture is mixed in the chamber 66 and passes downwardly through the bore 70, through the annular space between the needle 76 and the wall of passage 72, and through the port 60.

Means are provided for shutting off the idling fuel mixture to the port 60. This means comprises a ball valve 88 in the chamber 66, said ball being of smaller diameter than said chamber. The ball 88 is yieldingly urged upwardly'by a spring 89 disposed in the bore 70, the ball normally seating in a large opening 90 provided in the plate 68 between the openings 68a. The openings 68a provide forthe passage of fuel and air into said chamber 66 when the ball is seated in the opening 90. The ball 88 is adapted tobe pulled onto a seat 91 at the entrance to the bore 70 to, thereby cut off the idle fuel mixture to said port 60. This seating of the ball on seat 91 will take place when there is a manifold vacuum of, for example, approximately 24 inches of mercury, a condition which will occur during periods of fast deceleration. If desired, the valve 88 may be pulled onto its seat 91 by any other predetermined vacuum. Thus a saving of fuel as well as a reduction in the discharge of contaminants into the air from the engine exhaust will be effected as a result of this automatic shut off of the idling fuel.

The main fuel system of the carburetor includes provision for introducing fuel into air stream passing through the throat of the venturi 34 according to the suction action developed where the fuel enters the venturi. This may be accomplished by having one or more points of entrance of the fuel at the venturi throat, according to the requirement of the particular engine. One way in which the main fuel supply may be introduced into the venturi, including, as here shown, a main metering jet which comprises a tube having its outer end press fitted or otherwise secured in an opening provided therefor in the thickened wall of the air horn section 24. This outer end of the tube or jet 100 receives fuel from the chamber 52 by way of a passage 101 in the housing 53. The jet 100 extends into the venturi 34 and the discharge end of said jet is undercut at 103 and discharges adjacent the axis of said venturi and at the throat thereof. The jet 100 thus discharges into the air stream of the carburetor at the region of maximum suction at the venturi throat, the undercutting of the inner end of the jet increasing the suction at the discharge end of said jet.

As shown in Fig. 7, fuel for power operation is conducted from chamber 52 by way of opening 101 in the housing 53, a horizontal passage 106 in the air horn section, thence downwardly through passage 107 in said air horn section, through opening 108 in gasket 28a and into a downwardly extending passage 109 in the throttle body section 25. The lower end of the passage 109 connects with an inwardly extending horizontal passage 110 which communicates with a cylindrical recess 111 coaxial with the throttle shaft 37 and closed by a cover 111a secured to the throttle body section by screws 111b. Secured to the adjacent end of said shaft 37, which extends into said recess 111, is a movable valve member 112. This valve member is here shown as being semicircular although it may be of other shape and/or char acter to control an outlet port 114 spaced annularly in the recess 111 from the discharge end of the passage 110. When the throttle valve is in the closed position, the valve member 112 closes the port 114 but will progressively open the port 114 in accordance with the throttle opening and progressively close the port as the throttle valve is closed.

Port 114 is at the inlet end of an upwardly extending passage 115 formed in the throttle body section 25 to communicate with a passage 117 in the air horn section 24. The passage 117 leads into an annular space or chamher 118 between the outer wall of the venturi 34 and the adjacent wall 119 of the air horn section. The fuel discharged into said chamber 118 is discharged into the throat of the venturi by way of a plurality of annularly spaced ports 120 at said venturi throat. With this arrangement, the power fuel is discharged into the peripheral portion of the air stream at the throat of the venturi, whereas the main jet 100 will discharge fuel into the center of the air stream, thereby providing a better proportioned air-to-fuel mixture.

The power fuel valve 112 starts to uncoverthe-port 114, for example, at approximately 10 degrees of throttle opening, although the valve 112 may be opened at any other desired throttle valve position.

With reference to the foregoing description and accompanying drawings it will be apparent that a carburetor embodying the present invention is characterized by the advantages asfollows:

(1) Simplicity of construction, compactness and a minimum of movable parts, as well as but one adjusting means operable solely to regulate to idling speed;

(2) An automatic proportion of fuel-to-air resulting in fuel economy and increased engine efficiency.

(3) Ease of installation due to compactness, simplicity of construction and reduced bulk and weight.

(4) Additional fuel economy and the discharge of a minimum of exhaust pollutants due to the automatic shut-off of idling fuel incident to fast deceleration.

We claim:

1. In a liquid petroleum gas carburetor having an induction passage; a throttle shaft rotatably mounted in said induction passage; a throttle valve mounted on said shaft for controlling flow of fluid through said induction passage; a venturi in said induction passage anterior to said throttle valve; a main fuel jet extending into said venturi and having its discharge end positioned to discharge at substantially the axial center of said venturi; there being a plurality of annularly spaced jet ports at the throat of said venturi; means providing a first fuel passage for connection of said jet with a source of gaseous fuel; means providing a second fuel passage for connection of said jet ports with said source of gaseous fuel; valve means in said second passage for controlling the supply of fuel to said ports; said valve means mounted on said shaft to open said second passage only when the throttle valve is moved from idling position into a predetermined open position; an id'ing system including means providing a third fuel passage adapted to be connected with said fuel supply source and having a discharge port below the throttle valve when the latter is in the idling position; manual means in said third passage for adjusting the supply of idling fuel mixture to said discharge port; and normally open valve means in said third passage arranged to shut off the flow of fuel to said discharge port responsive to a vacuum of predetermined value at said idle system discharge port.

2. In a liquid petroleum gas carburetor having an induction passage: a throttle shaft rotatably mounted in said induction passage; a throttle valve mounted on said shaft for controlling flow of fluid through said induction passage; a venturi in said induction passage anterior to said throttle valve; a main fuel jet extending into said venturi and positioned to discharge at substantially the axial center of said venturi; there being a plurality of annularly spaced jet ports at the throat of said venturi; means providing for connection of said jet with a source of gaseous fuel; means providing a fuel feed passage leading to said jet ports; and valve means mounted on said shaft and operable in said fuel feed passage to control the supply of fuel through said fuel feed passage to said jet ports in accordance with the throttle valve position; said valve means opening to supply fuel to said jet ports when said throttle valve is moved past a predetermined open position. a

3. In a liquid petroleum gas carburetor having an in duction passage: a throttle shaft rotatably mounted in said induction passage; a throttle valve mounted on said shaft for controlling the flow of fluid through said induction passage; a venturi in said induction passage anterior to said throttle valve; a main fuel jet extending into said venturi and having its discharge end positioned to discharge at substantially the axial center of said venturi; said venturi having a plurality of annularly spaced jet ports at its throat; means providing for connection of said jet with a source of gaseous fuel; means providing a fuel feed passage leading to said jet ports; and valve means operable in said fuel feed passage for controliing the supply of fuel passing through said fuel feed passage to said jet ports responsive to operation of said throttle valve.

4. In a liquid petroleum gas carburetor having an induction passage: a throttle valve operably mounted in said induction passage for controlling flow of fluid therethrough; a venturi in said induction passage anterior to said throttle valve; a main fuel jet in said venturi arranged to discharge fuel from a side wall of the venturi into the throat of said venturi; there being a plurality of jet ports between the ends of said venturi for discharging fuel into said passage; means providing for connection of said jet orifice with a source of fuel; means providing a fuel feed passage leading to said jet ports; and valve means operable in said last named passage for controlling the supply of fuel passing through said feed passage to said jet ports in accordance with the throttle valve position.

5. In a liquid petroleum gas carburetor having an induction passage: a throttle valve operably mounted in said induction passage; a venturi in said induction passage anterior to said throttle valve; a fuel system discharging into said venturi; an idling system including a mixing chamber adapted to be connected with a source of vaporized liquid petroleum gas; there being an air passage leading to said chamber from a point in said induction passage anterior to said throttle valve; said idling system having a discharge port below one edge of the throttle valve when the latter is in the idling position; said port being connected with said chamber; and normally open valve means operable to shut off the flow of idling fuel mixture to said discharge port responsive to a vacuum of a predetermined value at said port.

6. In a liquid petroleum gas carburetor having an induction passage; a throttle valve operably mounted in said induction passage; a venturi in said induction passage; a fuel system discharging into said venturi; an idling system adapted to be connected with a source of vaporized liquid petroleum gas and a source of air, said idling system having an idling fuel-air mixture discharge port below the edge of the throttle valve when the latter is in the idling position; a valve member for controlling the supply of fuel to said port; and resilient means urging said valve member to a position permitting flow of the idling fuel mixture to said port; said valve member yielding to permit closing of said valve means responsive to vacuum of a predetermined value in said passage.

7. In an idling system for a petroleum gas carburetor: means providing walls defining an induction passage controlled by a throttle valve operably mounted in said induction passage; said walls having a passageway adapted to be connected with a source of vaporized liquid petroleum gas and a source of air, said passageway having a discharge port below the throttle valve when the latter is in the idling position; and normally open valve means operable to shut off flow of idling fuel responsive to vacuum of a predetermined value in said passage.

8. In a liquid petroleum gas carburetor having an induction passage controller; a throttle valve, and a pair of idling system passages, one of said idling system passages being adapted to be connected with a source of vaporized liquid petroleum gas; the other of said idling system passages being adapted to be connected with a source of air for mixture with said gas; said idling system having a discharge port connected with said idling system passages and operable to discharge mixed fuel and air into said induction passage when the throttle valve is in the idling position; and means operable by vacuum of a predetermined value in said induction passage for shutting off flow of the fuel mixture to said port.

9. A liquid petroleum gas carburetor having an induction passage; a throttle valve in said induction passage; a rotatable throttle shaft journalled in the walls of said carburetor; said throttle valve being mounted on said shaft; a venturi in said induction passage upstream of said throttle valve; said venturi having a plurality of jet ports at the throat thereof; a chamber adapted to receive gaseous fuel from a source of fuel at relatively low pressure; a main metering jet of fixed size, said jet comprising a tube receiving fuel from said chamber and extending into said venturi with the inner end thereof arranged to discharge fuel at substantially the axis of said venturi;

passage means in said walls connecting said chamber with the jet ports in said venturi throat; said passage means including a cylindrical recess having an inlet from said chamber and an outlet to the part of said passage means leading to said jet ports; a valve member secured to said throttle shaft rotatable therewith for controlling flow of fuel through said recess, said valve member closing said outlet from said recess until the throttle valve has reached a predetermined open position and thereafter progressively opening in correspondence to the increased opening of said throttle valve; an idling fuel system including fuel passage means connected with said chamber and having a mixing chamber, an air passage having its inlet adjacent the inlet of the induction passage and connected with said idling fuel mixing chamber, an idling fuel mixture passage from said chamber discharging inwardly of one edge of the throttle valve when the latter is in the substantially closed position, an adjustable metering valve for the idling fuel mixture passage; a vacuum responsive valve member in the latter passage; and resilient means urging said valve member in the opening direction.

10. In a liquid petroleum gas carburetor having an air horn section and a throttle body section with an induction passage through said sections; a throttle valve mounted in the portion of the induction passage in said throttle body section; a rotatable throttle shaft journalled in the walls of said carburetor and carrying said throttle valve; a venturi in said induction passage upstream of said throttle valve; said venturi having a plurality of annular spaced ports at the throat thereof; a chamber adapted to receive liquid petroleum gas from a source of said gas; a main metering jet tube receiving fuel from said chamber and discharging into said venturi; said throttle body section having a recess coaxial with said shaft and having an inlet connection with said chamber and an outlet connected with said ports in said venturi throat; and a movable valve member secured to said throttle shaft and normally closing said outlet, said valve member beginning to open said outlet when the throttle valve has reached a predetermined open position; further opening of said throttle valve effecting corresponding opening of said outlet.

11. In a liquid petroleum gas carburetor having an induction passage controlled by a throttle valve; said carburetor having an idling fuel system including a mixing chamber; an idling fuel inlet passage leading into said chamber; an .air passage leading from said induction passage to said mixing chamber; an idling fuel mixture passage leading from said mixing chamber to said induction passage for discharging fuel inwardly of the edge of the throttle valve when the latter is in the substantially closed position; an adjustable metering valve for the idling fuel mixture passage; a vacuum responsive valve member in said idling fuel mixture passage; and calibrated yielding means urging said suction responsive valve member in the opening direction.

12. In a liquid petroleum gas carburetor having an induction passage controlled by a throttle valve; said carburetor having an idling fuel system including an idling fuel inlet passage, a mixing chamber receiving fuel from said inlet passage, an air passage connected with said idling fuel mixing chamber, an idling fuel-air mixture passage leading from said chamber and discharging in said induction passage inwardly of one edge of the throttle valve when the latter is in the substantially closed position, a vacuum responsive valve member in the latter passage operable to shut off flow of the idling mixture into said induction passage incident to vacuum of a pre determined value in said induction passage; and spring means maintaining said valve member in open position while said throttle valve is in idling position and the vacuum in said induction passage is other than said predetermined value.

13. In a liquid petroleum gas carburetor having an induction passage: a throttle shaft rotatably mounted in said carburetor; a throttle valve mounted on said shaft for controlling the flow of fluid through said induction passage; means operable in said induction passage for developing therein a region of relatively high suction; a main fuel jet extending through a side of said passage and having its discharge end positioned to discharge into said induction passage at a region of relatively high suction; means providing for discharging jets of fuel at a plurality of locations about the periphery of the airstream in said induction passage at said region of relatively high suction; means providing a fuel feed passage leading to said last named means; and valve means controlling the supply of fuel through said fuel feed passage means responsive to predetermined rotative movement of said shaft.

14. In a liquid petroleum gas carburetor having an induction pass-age: means providing annularly spaced jet ports about the periphery of said induction passage; a throttle shaft rotatably mounted in said carburetor; a throttle valve mounted on said shaft for controlling the flow of fluid through said induction passage; fuel passage means for receiving gaseous fuel from a source of said fuel and delivering fuel to said annularly spaced jet ports; and means including a valve on said shaft operatively connected with said fuel passage means for controlling the supply of fuel to said jet ports responsive to predetermined rotation of said shaft.

15. In a liquid petroleum gas carburetor having an induction passage: a throttle valve operably mounted in said induction passage for controlling flow of fiuid there through; a venturi in said induction passage anterior to said throttle valve; a main fuel jet extending into said venturi and having its discharge end positioned in said venturi at a region of relatively high suction; there being a plurality of jet ports for discharging fuel into said venturi at said region; means providing for connection of said jet and said jet ports with a source of fuel; and valve means cooperable with said last named means for controlling the supply of fuel to said jet ports in response to predetermined movement of the throttle valve.

16. In a liquid petroleum gas carburetor having an air horn section and a throttle body section with an induction passage through said sections; a throttle valve mounted in the portion of the induction passage in said throttle body section; a rotatable throttle shaft journalled in the walls of said carburetor and carrying said throttle valve; a venturi in said induction passage upstream of said throttle valve, said venturi having a plurality of annularly spaced ports at the throat thereof; a chamber adapted to receive liquid petroleum gas from a source of said gas; a main metering jet comprising a tube receiving fuel from said chamber and extending into said venturi with the inner end thereof discharging at substantially the axis of said venturi; said throttle body section having a recess coaxial with said shaft and having an inlet connection with said chamber and an outlet connected with said ports in said venturi throat; and a movable valve member secured to said throttle shaft and normally closing said outlet, said valve member beginning to open said outlet when the throttle valve has reached a predetermined open position; further opening of said throttle valve effecting corresponding opening of said outlet.

17. In a liquid petroleum gas carburetor having an induction passage: a throttle shaft rotatably mounted in said carburetor; a throttle valve mounted on said shaft for controlling the flow of fluid through said induction passage; means operable in said induction passage for developing therein a region of relatively high suction; a main fuel jet having its discharge end positioned to dis charge at substantially the axial center of said suction development means; fuel passage means for discharging at a plurality of locations about the periphery of the airstream in said suction developing means at said region of relatively high suction; and means including a valve operable in said fuel passage means for controlling the supply of fuel through said fuel passage means in response to predetermined rotative movement of said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,641,332 Holley Sept. 6, 1927 10 Sartell Ian. 11, 1938 Ericson July 13, 1943 Coffey Feb. 15, 1944 Winkler Oct. 28, 1952 Hieger Nov. 11, 1952 FOREIGN PATENTS France Feb. 1, 1922 

1. IN A LIQUID PETROLEUM GAS CARBURETOR HAVING AN INDUCTION PASSAGE, A THROTTLE SHAFT ROTATABLY MOUNTED IN SAID INDUCTION PASSAGE, A THROTTLE VALVE MOUNTED ON SAID SHAFT FOR CONTROLLING FLOW OF FLUID THROUGH SAID INDUCTION PASSAGE, A VENTURI IN SAID INDUCTION PASSAGE ANTERIOR TO SAID THROTTLE VALVE, A MAIN FUEL JET EXTENDING INTO SAID VENTURI AND HAVING ITS DISCHARGE END POSITIONED TO DISCHARGE AT SUBSTANTIALLY THE AXIAL CENTER OF SAID VENTURI. THERE BEING A PLURALITY OF ANNULARLY SPACED JET PORTS AT THE THROAT OF SAID VENTURI, MEANS PROVIDING A FIRST FUEL PASSAGE FOR CONNECTION OF SAID JET WITH A SOURCE OF GASEOUS FUEL, MEANS PROVIDING A SECOND FUEL PASSAGE FOR CONNECTION OF SAID JET PORTS WITH SAID SOURCE OF GASEOUS FUEL, VALVE MEANS IN SAID SECOND PASSAGE FOR CONTROLLING THE SUPPLY OF FUEL TO SAID PORTS, SAID VALVE MEANS MOUNTED ON SAID SHAFT TO OPEN SAID SECOND PASSAGE ONLY WHEN THE THROTTLE VALVE IS MOVED FROM IDLING POSITION INTO A PREDETERMINED OPEN POSITION, AN IDLING SYSTEM INCLUDING MEANS PROVIDING A THIRD FUEL PASSAGE ADAPTED TO BE CONNECTED WITH SAID FUEL SUPPLY SOURCE AND HAVING A DISCHARGE PORT BELOW THE THROTTLE VALVE WHEN THE LATTER IS IN THHE IDLING POSITION, MANUAL MEANS IN SAID THIRD PASSAGE FOR ADJUSTING THE SUPPLY OF IDLING FUEL MIXTURE TO SAID DISCHARGE PORT, AND NORMALLY OPEN VALVE MEANS IN SAID THIRD PASSAGE ARRANGED TO SHUT OFF THHE FLOW OF FUEL TO SAID DISCHARGE PORT RESPONSIVE TO A VACUUM OF PREDETERMINED VALUE AT SAID IDLE SYSTEM DISCHARGE PORT. 